Development of the Shape Functions for Fatigue Test Using Digital Image Correlation

Mechanical failure of a structure or a machine during the regular working conditions are often related to the fatigue damage. As a consequence, the structural integrity monitoring of a system has always been a laborious task in the field of engineering. Since the strain measurement is one of the most important predictors of fatigue life, a precise strain measurement method is therefore required. There are many strain measurement methods in fatigue analysis; namely strain gauge, brittle coating method, photoelastic-coating and other optical strain measurement methods. However, various advantages and disadvantages have been found in each of the method mentioned above. Hence, there is always a need to develop a precise and yet informative strain measurement method in mechanical testing. The objective of this study is to develop the first-order shape functions for fatigue test using the Digital Image Correlation technique. In this study, sub-pixel accuracy image correlation algorithm was developed by using MATLAB whereby the positions of the points were precisely selected by using the fine-tuned function. As a result, the first-order shape functions were determined by retrieving the information that is stored in the affine transformation matrix. The works presented in this paper were mainly focused on the development of the algorithms, together with the results and the discussions for the validation exercises. In conclusion, a good agreement was achieved and the newly developed algorithm was proven to be accurate.